The problem of unlawful copying of copyrighted computer software has plagued software publishers since the commencement of distribution of software on magnetic media, e.g., floppy disks. Personal computers, which are routinely equipped with the necessary peripherals to read and write floppy disks and software to enable copying the indicia stored on one floppy disk to another floppy disk or a fixed disk, are generally all that is needed to copy software in the form of executable computer programs stored on floppy disks.
The industry has tried several schemes to thwart unlawful copying. In one group of schemes, at least part of the software is stored on the disk by arranging the indicia in nonstandard sectors which standard copy software and/or disk reading devices are unable to reproduce. In another group of such schemes, the floppy disk on which the software is stored is physically altered at predetermined regions, e.g., by burning holes in the magnetic coating, or the magnetism of the coating is weakened at predetermined regions. Unfortunately, the foregoing schemes have often made the software more problematic and difficult to use. Legitimate copying by lawful owners for backup purposes has also been made difficult if not impossible, often leaving the owners with useless disks for which they have paid large sums.
Another protection scheme tries to make a program operable on only one computer. This scheme requires that a unique readable device, e.g., a ROM chip, be installed in a personal computer before the software, which includes a program to read an identity code stored in the ROM, will function on the machine. This is a costly and unpopular proposition insofar as it requires that all PCs be fitted with a ROM, at a standard address, having an assigned code unique to the PC to which it is connected. This requires the mutual cooperation of virtually all PC manufacturers, many of whom are understandably unwilling to increase their costs and prices in the absence of any perceivable economic benefit.
Similar problems with copying have been encountered by publishers and distributors of motion pictures recorded on video tape cassettes. Weakened synchronization signals intended to cross the threshold from adequate in legitimate copies to insufficient, in unauthorized copies, are also troublesome in that the legitimate copies sometimes exhibit the symptoms intended for the unauthorized ones.